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Hello all! Running into an issues on my 1990 2.5l tbi std shift wrangler and need some help. First a little background. I was in the middle of a full rebuild when I had to relocate, so my brother back in Ohio is completing the rebuild. He put the fully rebuilt and assembled (by machine shop) motor in. I bought every sensor on the motor to replace, as well as new injector. Everything on the motor is new except the fuel pressure regulator and intake. A year ago I put a new fuel tank and pump/sending unit and filter in also.
Now the problem.....My brother has everything together. It fires right up and idles great. When he is easy on the pedal it runs fine, but when he really gets on the Gas hard it falls on it's face. He has checked the timing per the manual a few times and it's good. When he puts the timing lite on it while running he is at 11 degrees before tdc, which if I remember correctly was what it was at prior to the teardown. He is stumped.....hes a Ford guy so this is his first jeep motor....and I am fairly ignorant (most would agree strongly). He does not have a fuel pressure gauge to check it (he was going to check AutoZone borrow a tool deal this week to see if ones avail). Any suggestions would be greatly appreciated!

I recently bought a 1990 Jeep YJ with 4 cyl 2.5 TBI engine. The jeep runs great except during warm-up. It starts fine and runs and idles well initially. As soon as the temperature gauge begins to climb off the 100 degree mark, the engine begins hunting and surging and usually stalls. If I push down on the accelerator and run it to 1000+ rpm, I can get the engine to heat up to operating temperature. At that point (~160-170F) the idle becomes stable again. So far I haven't done a lot of troubleshooting but have checked the EGR valve, changed rotor/cap, air filter, and fuel filter with no success. I'm wondering if it might be a bad O2 sensor that's slow to heat up which will be the next thing I check/replace. Any ideas or help is much appreciated!

I hate to bring this up again, but I need help. I have a 1990 2.5 TBI wrangler that is killing me! I say I've been throwing parts at it, but given it's age everything I've done was either bad or well on its way. Now that almost everything has been replaced including the IAC I need help adjusting it. I assumed the IAC was in the correct position when I replaced it, but I'm suspect the PO had adjusted it when some of these parts I replaced went bad or possibly when they plated off the EGR (I replaced the egr and cleaned the egr tube) and now I find myself trying to adjust the IAC. I've adjusted it twice. The first time I was very close, but was not perfect so I adjusted it a turn more and it's acting up again. I've ready your very helpful advice, but call me slow I could use a bit more help or even pictures on how to do it the way you describe. The adjustments I made were before I found this page and I was told to just unplug it adjust it to 3500 rpm turn it off, plug it in, start it up for a minute then reset the ECU and I'd be good to go. Which is "close" to what I read here but miles away too. It did make it much better, but one more turn and it's back stalling out again. Can anyone give me pictures or better yet a video? I've hardly been able to drive the jeep since I purchased it.

T-shooting an intermittent starting problem. About 80% of start-ups are perfect. When failing to start, it will turn over and over, but won't fire up. Sometimes starter fluid will cause it to fire up and then it runs fine, but that's only 50% effective. The rest of the time, only push-starting will work, but push-starting does work every time. Most obvious assumption is fuel problem, but fuel system checks out fine (replaced almost everything over time anyway). Ignition/electrical is fine. Also, the problem seems to be completely independent of outside and engine temperature.
I started reading about ECU inputs, and discovered that during startup, an engaged WOT switch causes ECU to cut off fuel because ECU thinks it will flood the engine. The WOT switch is worn, but shouldn't prevent starting if disconnected. Would any other ECU inputs prevent fuel flow during start-up if their signals are outside normal limits? Service manual says during "Ignition On", CTS, MAT and MAP sensors begin providing input to ECU, but doesn't list MAT or MAP sensors during actual start-up. See attached page. So which sensors matter to ECU for start-up fuel supply calculations or decisions?
Also, during push-starts, the ignition (key switch) is in the Run position, and not the Start position, which changes the ECU inputs, too.
My shop has a DRB II diagnostics reader, but unless they hook it up when it happens to be misbehaving, shouldn't everything check out ok? Unfortunately, I've never been able to get it to fail at the shop.
I also tried replacing the fuel relay. I also noticed that it is no longer cycling the ISA motor when it fails to start. It used to, but I can't figure out why it did that anyway.
What are my next moves?
Might be trying to oversimplify this, but what kind of intermittent problem would occasionally prevent a normal startup, but NEVER prevent a push-start from succeeding?

I put a new 2.5l into the jeep and it only has 400 miles. It was running great till suddenly the issues popped up again. I hooked the scanner up and saw that the short term trim was ridiculously high. Its reference point at idle is 128 and its running at 180. The long term trim is at 109. the injector pulse is 2.0. The o2 sensor was reading no higher than 500mv.

Hi,
I have a 1988 Jeep Yj 2.5 with the renix computer.
My last stop before I drive this thing off a cliff is here. I should have come here first. I hope one of you can help me. I love my Jeep but am so frustrated with it right now.
Problem: Jeep is running super rich. I do not think it is ever coming out of closed loop.
Points to know:
- O2 sensor is recognizing that the jeep is rich. Volts sit between .94V and .99V
JEEP RUNS AWESOME. No loss of power. No hesitation. Idles between 900 and 750
- Fuel smell coming from the tailpipe
Emissions high on HC and CO
Things I have tried:
-Replaced o2 sensor
-replaced fuel pressure regulator
-replaced CTS
replaced ISA
replaced ECU
replaced MAP
Replaced MAT
checked return fuel line for blockage.
Had Head rebuilt. Vacuum was fluctuating and needed new valve guides. Was hoping this was impacting the MAP sensor. Nope
I have gone through entire FSM diagnostic tree. The only thing that failed was the MAT sensor resistance never got down to 150ohms. Always stayed above 300.
I even paid a mechanic $600 to try and uncover the problem. He confirmed it was not coming out of closed loop. Recommended changing the ECU. Which I did.
I hope someone can help.
Thank you all in advance.
Carlos

Hello im new to this i am from hawaii i have a 1989 jeep wrangler and have a brand new motor installed it had an idle problem so i changed the tps set it in between 4.6 and 4.7 on the multimeter which is what the dealer said to set it as and it runs for ten minutes and as soon as i tal the gad it sputter then dies any ideas ?

I'm at my wits end troubleshooting my lil 2.5L engine. I googled and found your page from about a year ago. 1990 jeep wrangle 25l engine timing.
Today I thought about timing. It misses, like running on only 2 cylinders when at low speed and and only pulling slightly. As I move into mid and upper rpm range it stops missing. I still do not have much acceleration but at least it stops missing. I've check and/or changed every sensor it has. TPS is only rough since I have not gotten my laser tach to work yet.
In checking fuel I have only 10 psi so I know that's a problem. This started about a month after the SMOG guy changed the O2 sensor to pass smog. I've check the voltage when hot and it's within spec. I also had massive exhaust gasket leak so I cleaned the surfaces and replace the gasket.
I'm a machine mechanic from way back in the Navy so I'm not just a new mechanic. I just can't quite figure this one out. I'll check timing tomorrow.
Lowell

Thanks for the engine information.
Ok .... update for today. I'm really not finding a vacuum leak and before I build a smoke machine there's been this gnawing in the back of my mind to check the valve timing. I found this pdf manual http://oljeep.com/JeepEngines.pdf and on page 63 it tell how to check valve timing. So I removed all the plug, it was easier to rotate by removing all the rocker bridges, set up a dial indicator on the #1 intake push rod and checked .... Hmmm the dial moved .010 but I don't see the index mark anywhere (????) ... oh, there it is 3 inches to the left, or 3 inches BTDC ... really???? Guess I'll pull the timing cover and check it out.